Glossary (plain English)

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Jump here whenever a word feels fuzzy. Definitions stay public and field-fundamental --- not paper-specific results.

Term	Plain English
AQFP	Adiabatic Quantum Flux Parametron --- logic family using multiphase AC excitation and adiabatic switching.
Bias current	Steady current that holds a Josephson junction near its switching threshold so a small trigger can launch an SFQ pulse.
Cryogenic	Cold enough for the device (often ~4 K for Nb SFQ; millikelvin for many qubits) --- not automatically "liquid nitrogen cold."
Cryo-CMOS	CMOS electronics operated cold; sibling/hybrid path beside Josephson logic.
β_C (McCumber)	Damping parameter. Small → overdamped (pulse); large → underdamped (can latch).
Clock window / epoch	Time slot in which the presence or absence of an SFQ pulse means logic 1 or 0.
Confluence	Cell that merges pulses from two lines onto one (with timing rules).
Concurrent-flow clocking	Clock pulses travel roughly in the same direction as data.
Counter-flow clocking	Clock pulses travel roughly opposite to data.
Critical current $I_c$	Largest supercurrent a Josephson junction can carry before it switches.
Critical temperature $T_c$	Temperature below which a material can superconduct.
DFF (RSFQ)	Data flip-flop --- stores one flux quantum until a clock pulse reads it out.
ERSFQ	Energy-efficient RSFQ --- pulse logic with bias networks aimed at near-zero static resistor power.
Flux quantum ${\Phi }_0$	Smallest stable flux packet in a superconducting loop; $\approx 2.07\text{mV}\cdot \text{ps}$.
Fluxon	A discrete flux quantum treated as a mobile information token.
4JL / Suzuki stack	Latching underdamped junction stacks used to boost voltage for I/O.
Gate-level pipelining	Almost every logic cell is also a timed pipeline stage (RSFQ default).
Ground island	Circuit block with its own local ground potential (needed in serial biasing).
JTL	Josephson Transmission Line --- active chain that regenerates SFQ pulses.
Josephson junction (JJ)	Weak link between superconductors; heart of SFQ switching.
JAWS / Josephson voltage standard	Metrology uses of Josephson physics for accurate voltages (sibling branch to digital SFQ).
Latching	Junction stays at a large voltage until reset (often underdamped I/O).
Landscape (field)	Map of sibling disciplines: digital SFQ, SQUID sensing, metrology, detectors, quantum I/O, cryo-CMOS, EDA.
Overdamped	Junction emits a short pulse and returns to $V\approx 0$ (RSFQ gates).
Path balancing	Equalizing stage counts on reconvergent paths so pulses share an epoch.
Phase $\varphi$	Superconducting phase difference across a junction; a $2\pi$ slip ↔ one ${\Phi }_0$.
PTL	Passive Transmission Line --- long superconducting interconnect needing driver/receiver.
Qubit	Quantum bit --- physical system storing quantum information; superconducting qubits are one QC hardware platform (not classical SFQ).
Quantum computing	Field of information processing with quantum states; may use superconducting qubits and classical cryo helpers (SFQ/cryo-CMOS).
Quantum interference	Amplitudes add or cancel; QC algorithms boost useful outcomes and suppress others (algorithmic resource --- not classical SFQ pulse logic).
Quantum dot (qubit)	Semiconductor nanostructure qubit platform; closer to cryo-CMOS/semi story than to RSFQ.
Entanglement	Non-classical correlation among qubits used as a resource in multi-qubit algorithms (not how classical SFQ links gates).
Superposition	Qubit state combining basis states until measurement; enables rich multi-amplitude states in QC algorithms (not an RSFQ pulse token).
Neutral-atom qubit	Qubit platform using arrays of neutral atoms (e.g. optical tweezers); weak overlap with SFQ gates.
Photonic qubit	Qubit platform encoding information in light; often needs detectors (e.g. SNSPD) --- medium overlap via readout.
RCSJ	Resistively and Capacitively Shunted Junction model (JJ + $R$ + $C$).
RSFQ	Rapid Single Flux Quantum --- pulse-based superconducting digital logic family.
Serial biasing / current recycling	Reusing one bias current through series-stacked ground islands.
SFQ pulse	Picosecond voltage spike with area $\int Vdt={\Phi }_0$.
SNSPD / SSPD	Superconducting nanowire (single-photon) detector --- sibling branch often needing cryogenic readout.
Splitter	Cell that copies one SFQ pulse onto two outputs (fanout).
SQUID	Superconducting Quantum Interference Device --- loop with junctions; flux sensor / building block.
SQUID stack	Series SQUID stages that add voltage for interface drive.
Topological qubit	Research platform aiming at topologically protected qubits; awareness-only for this SFQ curriculum.
Trapped-ion qubit	Qubit platform using ions in electromagnetic traps with laser control; QC sibling, weak SFQ overlap.
STA	Static timing analysis --- check setup/hold-like windows without full pattern simulation.
Supercurrent	Current through a superconductor with essentially zero DC resistance.
Underdamped	Junction can latch at large voltage; used in some drivers, not typical RSFQ gates.
VT-RAM	Vortex transitional memory --- stores bits as flux/vortex states in loops.

More wording elsewhere: prefer the linked fundamentals / bridges when a one-liner is not enough.